Not even close. Most of the greenhouse effect is due to water vapor, which is about 100 times as abundant in the atmosphere as CO2 and thus has a much larger effect.

Oh, really?

Suppose you have a planet with an atmosphere composed exactly like Earth’s, with water oceans and a yellow dwarf sun as well. Thus, its atmosphere would indeed have both CO2 and H2O, complete with clouds and typical weather patterns.

Suddenly, all the CO2 is removed from the atmosphere. Without the greenhouse effect it provides, the temperature drops quickly. The relative humidity skyrockets. In some areas, it exceeds 100%, and when that happens, clouds form, increasing the planet’s cloud cover. The clouds block and reflect the sunlight, further cooling the air below them as well as the surface. Precipitation results and the atmosphere loses most of its H2O as well. So the atmosphere becomes colder and drier, until finally the planet is locked in an ice age, which it can never recover from unless CO2 is added. Even the oceans will be frozen up.

Now, we add the CO2 back. With CO2 trapping heat once more, ice begins to melt. Then water begins to evaporate. As water evaporates, the H2O kicks in with its own greenhouse effect, resulting in more ice melting. Eventually, the oceans are restored, and the atmosphere returns to what it was.

H2O alone on Earth cannot keep the planet warm enough to sustain life, because at certain temperatures and concentrations in the atmosphere it forms clouds which act as cooling agents, and on land below a certain temperature it forms ice, which also reflects light. CO2 must be the trigger for the greenhouse effect of both substances to operate properly on Earth. Quite simply, those ICECAP “experts” are either lying or just idiots!